1. Field of the Invention
This invention relates to an apparatus for reading images from a photographic film disposed on an image reading optical path.
2. Description of the Related Art
An apparatus for reading images from photographic film is known as a film scanner which irradiates the film with light from a light source. Images recorded on the film are read usually by detecting light transmitted through the film with a CCD sensor or the like.
The primary function of the photographic film reading apparatus is to read images from photographic film as noted above. In recent years, however, it has been proposed to improve image quality by detecting also scratches or dust made or adhering to the photographic film as images, determining positions of the scratches or dust on the film, and correcting photo images affected by the scratches or dust.
A technique for detecting such scratches and dust on photographic film is disclosed in U.S. Pat. No. 5,266,805 (correspondence to Japanese Patent Laying-Open Publication H6-28468), for example. According to this prior technique, scratches and dust on photographic film are identified from an image read from the film by using infrared light and an image read from the film by using visible light. This technique, in general, utilizes phenomena that visible light is modulated both by an image recorded on photographic film and by scratches and dust made or adhering to the film, whereas infrared light is modulated by the scratches and dust through scattering, but is not influenced by the image on the film.
A similar technique for detecting such scratches and dust on photographic film is disclosed in Japanese Patent Laying-Open Publication H9-163133. This technique uses dark field illumination instead of infrared light illumination.
An image other than one acquired by visible light is required to detect scratches or dust on photographic film. In the former of the conventional techniques, light for irradiating photographic film is successively switched by means of a rotating filter between visible light and infrared light. A visible image and an infrared image are obtained at different points of time. In the latter technique, an optical system for obtaining a visible image and one for obtaining an image different from the visible image are arranged in separate locations to obtain the two types of images sequentially.
However, each of the above prior techniques detects a visible image and a different image (infrared image) at different points of time, which results in an extended time required for detecting the images. Where two optical systems are arranged in separate locations, the two types of images could be associated in an inaccurate positional relationship. Further, the two separate optical systems have the drawback of enlarging an apparatus configuration.
This invention has been made having regard to the state of the art noted above, and its object is to provide a photographic film image reading apparatus for detecting a visible image and an infrared image speedily, while enabling an accurate determination of a positional relationship between the two images.
The above object is fulfilled, according to this invention, by an apparatus comprising a visible light sensor for detecting a visible image based on visible light irradiating a photographic film, and an infrared light sensor for detecting an infrared image based on infrared light irradiating the photographic film. The visible light and infrared light are emitted from a light source to travel simultaneously along an image reading optical path and irradiate the photographic film.
The light source emits visible light and infrared light so that the two types of light concur in the film image reading optical path to irradiate the photographic film. The visible light sensor detects a visible image of the photographic film, while the infrared light sensor detects an infrared image thereof.
With this construction, since visible light and infrared light concur in the film image reading optical path, a visible image and an infrared image of the photographic film may be acquired by a single photometric stage, and that at the same time. Thus, a photographic film image reading apparatus is provided which is capable of detecting both a visible image and an infrared image promptly while accurately determining a positional relationship between the two images.
In an embodiment of this invention, the visible light sensor and infrared light sensor are disposed in different positions, the film image reading optical path including an optical path branching unit for directing the light emitted from the light source toward the visible light sensor and the infrared light sensor. Preferably, the optical path branching unit is arranged to direct the visible light toward the visible light sensor and the infrared light toward the infrared light sensor.
With this construction, the optical path branching unit disposed on the film image reading optical path directs the visible light toward the visible light sensor, and the infrared light toward the infrared light sensor.
The visible light sensor which detects visible images and the infrared light sensor which detects infrared images have a similar construction as sensors, and may therefore be integrated. However, a system that handles both visible images and infrared images is not necessarily common. It is difficult to manufacture an image reading sensor integrating an infrared light sensor and a visible light sensor at low cost.
Thus, the optical path branching unit is placed on the film image reading optical path as described above. This enables the visible light and infrared light to concur in the same optical path even where the visible light sensor and infrared light sensor are separate entities.
As a preferred embodiment for directing the visible light toward the visible light sensor and the infrared light toward the infrared light sensor, it is proposed that the optical path branching unit be formed of a cold mirror. A cold mirror is often used as a reflector for a lamp to reflect visible light and pass infrared light in order to avoid overheating of an illuminating optical path. Design load may be lightened by utilizing an existing cold mirror as the optical path branching unit.
It is advantageous to provide an infrared light cut filter between the cold mirror and the visible light sensor. Where the cold mirror is used to reflect visible light, part of infrared light could mix into the light reflected by the cold mirror. Such part of infrared light may be intercepted reliably by the infrared light cut filter to prevent overheating of the visible light sensor and detect visible images properly. Moreover, this infrared light cut filter is disposed in a portion of the optical path used only for guiding the visible light. Thus, a conventional infrared light cut filter may be used as it is, without increasing design load.
In a preferred embodiment of this invention, the image reading optical path includes an infrared light cut filter and a light adjustment filter arranged between the light source and the photographic film, the light adjustment filter adjusting the light to a predetermined color balance before irradiating the photographic film. Wavelength characteristics of light transmittance of the infrared light cut filter and the light adjustment filter combined allow transmission of infrared light in a set wavelength range, and cut infrared light outside the set wavelength range, in order to enable image detection by the infrared light sensor.
Not only an infrared light cut filter but a light adjustment filter usually is designed to intercept infrared light. In order to detect an infrared image of photographic film, the infrared light cut filter and light adjustment filter of such design must be removed from the film image reading optical path. Otherwise, these filters will impede detection of the visible image of the photographic film, and cause overheating of components arranged on the optical path. Thus, in order to enable image detection by the infrared light sensor, the wavelength characteristics of light transmittance of the infrared light cut filter and light adjustment filter combined are made to allow transmission of infrared light in a set wavelength range, and cut infrared light outside the set wavelength range. The infrared light of wavelengths not required by the infrared light sensor is cut. Consequently, the photographic film image reading apparatus intended to detect infrared images can prevent overheating of the photographic film and optical elements. In cutting the infrared light outside the set wavelength range noted above, it is not absolutely necessary to intercept all infrared light outside that wavelength range. A wavelength range may be set properly for cutting infrared light to restrain temperature increases of the optical elements within a permissible range. In addition, the characteristics for cutting such infrared light may be realized by the combination of the infrared light cut filter and light adjustment filter. Both of the filters need not have infrared light cutting characteristics.
It should be, noted here that the photographic film image reading apparatus, in reality, is required to cope with varied sizes of photographic film and varied print sizes. Thus, there exist strong demands for the visible light sensor to read images of the photographic film in various magnifications. Where reading magnification on the visible light sensor system side is made variable, lens power on the infrared light sensor system side must also be made variable to form the images of the photographic film on the light-receiving plane of the infrared light sensor in a corresponding relationship to the visible images.
Such a variable magnification lens, typically, is a zoom lens. The zoom lens is designed to have a fixed focal position regardless of magnifications. However, such a design is made by taking visible light into account. Inventors herein have found that, when infrared images are read by using such a lens optimized with respect to visible light, the wavelength dependence of refractive index results in excessive variations in the focal position occurring with variations in the magnification of the lens, thereby blurring the images. It is conceivable in this case to construct the infrared light sensor movable in the direction of the optical axis when the magnification is varied, to absorb the variations in the focal position. However, a complicated construction is required to move the infrared light sensor in the direction of the optical axis with high precision.
In another aspect of this invention, an apparatus of simple construction is provided which is capable of reading an excellent infrared image where lens power is variable. This apparatus comprises a light source for emitting visible light and infrared light into an image reading optical path to irradiate a photographic film, a zoom lens unit for the visible light and infrared light irradiating the photographic film, a visible light sensor for detecting a visible image based on the visible light from the zoom lens unit, an infrared light sensor for detecting an infrared image based on the infrared light from the zoom lens unit, and a focal position varying transparent element for shifting a focal position of the zoom lens unit along an optical axis, the focal position varying transparent element being movable to and from a position between the zoom lens unit and the infrared light sensor, wherein variations in the focal position occurring with variations in magnification of the zoom lens unit are corrected by movement of the focal position varying transparent element.
With this construction, when the magnification of the lens is varied to form an image of the photographic film on the light-receiving plane of the infrared light sensor, the focal position varying transparent element is moved to or from the position between the zoom lens unit and the infrared light sensor to shift the focal position along the optical axis.
The focal position is shifted by the focal position varying transparent element by an amount corresponding to a variation in the focal position due to a variation in the magnification of the lens. In this way, variations in the focal position occurring with variations in the magnification of the lens are corrected by movement of the focal position varying transparent element. Consequently, even when the magnification of the lens is varied, the focal position is present steadily on the light-receiving plane of the infrared light sensor. Infrared images are read reliably by a simple construction for moving the focus position change transparent element.
In a preferred embodiment of this invention, the focal position varying transparent element is formed of sheet glass. When the magnification of the lens is varied, this sheet glass is moved to or from the position between the lens and infrared light sensor.
When the sheet glass is inserted between the lens and infrared light sensor, the focal position shifts away from the lens, approximately depending on the refractive index and thickness of the sheet glass. Thus, the sheet glass is set to have a refractive index and thickness for shifting the focal position away from the lens by a distance corresponding to a variation in the focal position occurring with a variation in the magnification of the lens. In this way, variations in the focal position due to variations in the magnification of the lens may be corrected.
An aberration may be caused by the sheet glass placed between the lens and infrared light sensor. It is noted, however, that variations in the focal position due to variations in the magnification result in no serious aberration. Based on this perception, the focal position varying transparent element is formed of such a simple element as sheet glass.
A slight disagreement inevitably occurs with the position of an identical object (or identical part) in an image on photographic film, between image information acquired with the visible light sensor and image information acquired with the infrared light sensor. This invention proposes an apparatus and method set out hereinafter as a technique for rectifying this disagreement in a simple way.
The apparatus comprises a light source for emitting visible light and infrared light into an image reading optical path to irradiate a photographic film, a lens unit for the visible light and infrared light irradiating the photographic film, a visible light sensor for detecting a visible image based on the visible light from the lens unit, an infrared light sensor for detecting an infrared image based on the infrared light from the lens unit, a calibration chart having images recorded thereon to be readable with infrared light, the calibration chart being movable to and from a position for reading the photographic film, and a positional relationship determining device for determining, based on the images of the calibration chart read by the infrared light sensor, a positional relationship on images of the photographic film between image information acquired from the visible light sensor and image information acquired from the infrared light sensor.
The method comprises the steps of setting a calibration chart having images recorded thereon to be readable with infrared light to a position for reading the photographic film, forming images of the calibration chart on light-receiving planes of both a visible light sensor and an infrared light sensor through a lens unit, and determining a positional relationship on images of the photographic film between image information acquired from the visible light sensor and image information acquired from the infrared light sensor, by comparing image information on the calibration chart read by the visible light sensor and image information on the calibration chart read by the infrared light sensor.
When reading a visible image and an infrared image of photographic film, the calibration chart having images recorded thereon to be readable with infrared light is placed in the position for reading the photographic film. The images of the calibration chart read by the infrared light sensor are used to determine a positional relationship on the images of the photographic film between image information acquired with the visible light sensor and image information acquired with the infrared light sensor.
That is, Inventors have found that a slight displacement between image information acquired from the visible light sensor and image information acquired from the infrared light sensor is caused by a slight difference in magnification of the lens between a region of visible light and a region of infrared light. The displacement is corrected by detecting the slight difference in magnification with the calibration chart.
The images recorded on the calibration chart may have a length serving as a reference, for example. A magnification for the infrared light sensor may be determined accurately based on what length is detected by the infrared light sensor of the images having the reference length. It is not necessary to use the calibration chart for an accurate determination of the magnification on the visible light sensor side.
It is proposed as a preferred embodiment that the calibration chart is readable also with visible light, the positional relationship determining device determining a positional relationship on the images of the photographic film between image information acquired from the visible light sensor and image information acquired from the infrared light sensor, by comparing image information on the calibration chart read by the visible light sensor and image information on the calibration chart read by the infrared light sensor. That is, the positional relationship between visible image and infrared image is determined by using the images of the calibration chart acting as the reference read by both the visible light sensor and infrared light sensor. Thus, the visible image and infrared image are associated with increased accuracy.
In a preferred embodiment, the calibration chart is formed of a metal plate defining through grooves or through holes. The images of the through grooves or through holes formed in the metal plate may be read with infrared light accurately. Thus, the positional relationship between image information acquired from the visible light sensor and image information acquired from the infrared light sensor may be determined with increased accuracy.
In a preferred embodiment of this invention, the lens unit is a zoom lens unit, the positional relationship determining device determining, for each magnification set to the zoom lens unit, a positional relationship on the images of the photographic film between the image information acquired from the visible light sensor and the image information acquired from the infrared light sensor.
Sizes of photographic film from which images are read, and print sizes, may be accommodated in a flexible way by using the zoom lens unit to set or vary the magnification of the imaging lens system as noted above. Inventors have found that, when the magnification of the lens is varied, the positional relationship between image information acquired from the visible light sensor and image information acquired from the infrared light sensor varies also. Thus, by determining, for each magnification set to the zoom lens unit, the positional relationship on the images of the photographic film between the image information acquired from the visible light sensor and the image information acquired from the infrared light sensor, an adequate positional association of a visible image and an infrared image may be made even when the magnification of the lens is varied
Other features and advantages of this invention will be apparent from the following description of the embodiment to be taken with reference to the drawings.